In telecommunication systems, signals are transmitted over cables having balanced twisted pairs of wires. Typical cables have four pairs of twisted wires in them. For connecting wires to other cables or to other apparatus, connectors are mounted on the ends of the cables. Although connectors can be mounted in the field after the cables and wires therein are cut to the appropriate length for the particular installation, preferably, high performance connectors are preferably assembled in a controlled environment so they can be tested and qualified for use.
Due to advances in telecommunications and data transmissions, connectors, particularly including plugs, have become a critical impediment to good performance of data transmission at new, higher frequencies. Some performance characteristics, particularly near end crosstalk and return loss, degrade beyond acceptable levels at these higher frequencies.
One way to overcome this crosstalk problem is to increase the spacing between the signal lines. Another method is to shield the individual signal lines. However, in many cases, the wiring is pre-existing and standards define geometries and pin definitions for connectors making such changes to those systems is cost prohibitive. In this specific situation of communications systems, using unshielded twisted pair wiring cables is the only practical alternative.
When electrical signals are carried on a signal line or wire which is in close proximity to another signal line or other signal lines, energy from one signal can be coupled onto adjacent signal lines by means of the electric field generated by the potential between the two signal lines and the magnetic field generated as a result of the changing electric fields. This coupling, whether capacitive or inductive, is called crosstalk when the coupling occurs between two or more signal lines. Crosstalk is a noise signal and degrades the signal-to-noise margin (s/n) of a system. In communications systems, reduced s/n margin results in greater error rates in the information conveyed on the signal lines.
Performance requirements for modular plugs are defined in ANSI/TIA/EIA-568-B, “Commercial Building Telecommunications Cabling Standard”. In the Category 6 Addendum TIA-568-B.2-1 to that standard, the acceptable performance ranges are detailed in Section E.3.2.2, and summarized in Table E.3.
Additionally, in communications systems certain standards have been developed that define connector geometry and pin out definitions. Those standards were created prior to the need for high speed data communications, and have created a large installed base of wiring connectors. Additionally, those standards have created a need for connectors capable of maintaining the requirements of higher speed communications, while maintaining compatibility with original connectors.
The standard connector geometry and pin outs can generate a great deal of crosstalk at higher signal frequencies. Connectors addressing this problem include U.S. Pat. No. 5,432,484 to Klas et al and U.S. Pat. No. 5,414,393 to Rose et al, the subject matters of which are hereby incorporated by reference in their entirety.
U.S. Pat. No. 6,080,007 to Milner et al., and which is hereby incorporated by reference in its entirety, discloses a connector for a communications system. However, the rear sled 34 (FIG. 4) provides individual conduits for each wire passing therethrough. Additionally, the rear end of the rear sled is flush with the rear end of the plug housing, so that it cannot control the distance between the cable sheath and the rear sled.
U.S. Pat. No. 6,439,920 to Chen discloses an electronic connector for high speed transmission. The end of the cable sheath 30 (FIG. 3) is spaced from the point at which the wires enter the inserts tunnels 61-64 (FIG. 2) so the insert element restricts the spacing of the wires through the insert element, thereby preventing control of the crosstalk level.
In addition to the crosstalk reduction provided by the inventions of the above cited patents, crosstalk generated at the connection between the cable wires and the connectors, particularly the plug connectors has become significant. Variations in the placement of the wiring creates varying amounts of crosstalk. Additionally, the wires must be accurately and precisely located within the connector to facilitate termination by the insulation displacement contacts.
Thus, there is a continuing need to provide improved connectors for communications systems.